What does Exodus 9:23 mean?

The Lord has continually commanded Pharaoh to release Egypt's Hebrew slaves (Exodus 5:1; 7:16; 8:1, 21; 9:1). Each time was met with stubbornness (Exodus 5:2; 7:13–14, 22; 8:15, 19, 32; 9:7). So, God makes good on His threat to strike Egypt with a seventh catastrophe. This disaster is an epic hailstorm that will kill any living thing still out in the open (Exodus 9:18). Only those Egyptians who paid attention to the warning (Exodus 9:19) and the people of Israel (Exodus 9:26) will be spared.

In the Old Testament, hail is bārād' and the words for "lightning" and "fire" are berāqim' and ēs'. Flashes in clouds were probably always called "berāqim" (Exodus 19:16). Ground fires were usually labeled with ēs'. Here, Scripture says that "ēs'" ran down to earth. Many Hebrew references to fire in a divine context are probably descriptions of lightning bolts (1 Kings 18:38; Psalm 148:8; Job 1:16), though not all are (Exodus 3:2; 19:18). The next verse (Exodus 9:24) refers to the ēs' as "flashing," using a phrase that literally means "holding together" or "joining itself." This was a true "storm" of hail, including prolific amounts of lightning and thunder (Exodus 9:28). Despite how this plague is depicted in popular movies and television shows, it's not likely that meteors or flames were falling from the sky.

The ending summary here is the primary lesson sent by these supernatural plagues (Exodus 3:20). God worked through Moses, but God was the source of the storm's power. Egyptian idols are proven to be nothing but imagination. Because Pharaoh refuses to obey the Lord's message, the plagues bring judgment upon Pharaoh, his people, and his land.